Alveolar bone

ALVEOLAR BONE
www.indiandentalacademy.com

CONTENTS
•Introduction
•Development
•Parts of bone
•Functions of Alveolar bone
•Histology of alveolar bone
•Composition of bone
•Cells of Alveolar bone
•Bone modeling and remodeling
•Theories on bone resorption
•Clinical consideration www.indiandentalacademy.com

INTRODUCTION
 Definition : Alveolar process is the portion of
maxilla and mandible that forms and supports
tooth sockets
 Along with the periodontal ligament, cementum
and gingiva it provides the attachment of the tooth
to the respective jaw of the oral cavity.
 As they are tooth dependent structures the size,
shape, location and function of the teeth determine

DEVELOPMENT
Near the end of the 2nd
month of fetal life,
mandible and maxilla
form a groove that is
opened toward the
surface of the oral cavity

 Mandibular growth is principally attributed
to intramembranous osteogenesis,
augmented by focal endochondral
ossification at the condylar head, mandibular
angle, and coronoid process
 subsequent complex growth patterns include
synchronized ‘cortical drifting’ at the lateral
and medial periosteal surfaces leading to
forward and downward mandibular rotation
and expansion

 Mandibular growth is also dependent on
muscle attachments and tooth development
and eruption influence alveolar development.
 The maxilla arises from intramembranous
osteogenesis at two centers lateral to the
nasal capsule
 growth primarily occurs by apposition at
sutures that connect the maxilla to the
cranium and cranial base, augmented by
complex differential surface appositional and
resorptive patterns.

 Bony development in the infraorbital and
alveolar regions, in addition to the frontal,
zygomatic, and palatal processes, largely
appears to reflect the differential functions of
vision, respiration, olfaction, mastication,
deglutition, and speech, where the face
progressively grows ‘out from under the
cranium’

 As tooth germs start to develop, bony
septa form gradually. The alveolar process
starts developing strictly during tooth
eruption
 As the periodontal ligament is forming,
new bone is deposited around the
developing ligament fiber bundle.

 The Alveolar bone has its embriological
origin from the initial condensation of
ectomesenchyme around the early tooth
germ (Ten cate, 1997).
 The specific embryonic origin of bundle
bone is the dental follicle (Ten cate 1997)

Parts of Alveolar Bone
1.An external plate of cortical bone
( Haversian bone or compact bone)
2.Inner socket wall of thin compact bone
called alveolar bone proper (cribriform
plate)
3.Cancellous bone or Spongy bone
located between the above two. It is
found predominantly in the interdental
and interradicular spaces

Parts of Alveolar Bone

COMPACT BONE OR HAVERSIAN BONE
 Similar to compact bone anywhere else
(Haversian bone)
 Extends both on the lingual (palatal) and
buccal side
 Contains haversian and Volkman’s canals
(they both form a continuous channel of
nutrient canals)

ALVEOLAR BONE PROPER
 The compact or dense bone that lines the
tooth.
 Contains either perforating fibers from
periodontal ligament (Sharpey’s fibers) or
just compact bone
 Sharpey’s fibers embedded into the
alveolar bone proper

• Present at right angles or oblique to the
surface of alveolar bone and along the root
surface
• Because alveolar process is regularly
penetrated by collagen fiber bundles,
it is also called bundle bone. It appears more
radiodense than surrounding supporting bone
in X-rays called lamina dura www.indiandentalacademy.com

SPONGY BONE
 Spongy bone is composed of bone
spicules, also called trabeculae, of
varying shapes and sizes.
 The spaces between the spicules are
filled with marrow. The composition of
spongy bone (cells and matrix) is the
same as that of compact bone.

FUNCTIONS OF THE ALVEOLAR BONE
 Supporting structure of the teeth.
 Alvolar Bone of the maxilla and mandible
gives attachment to the muscles
 Provides a framework for the bone
marrow
 Acts as a reservior of the ions particularly
calcium

HISTOLOGY OF ALVEOLAR BONE
 They are composed of microscopic layers
or lamellae,
 Microscopically three distinct types of
layering are recognised.
 Circumferential
 Concentric
 Interstitial.

Bone Model showing Concentric and Interstitial Lamelle

Model of the Bone Showing Circumferential lamellae, fibrous Periosteum, Cellular
Periosteum And Osteon
Ten cate 1996

 Circumferential lamalle enclose the entire
adult bone forming its outer perimeter
 Concentric lamelle make up the bulk of the
compact bone and make up the metabolic
unit of compact bone called OSTEON

 An osteon is a cylinder of bone
oriented in the long axis of the bone
 In the center of each osteon there is a
Heversian canal lined by a single
layer of bone cells
 Each Haversian canal houses the
capilleries , Nerve fibers andwww.indiandentalacademy.com

 Present perpendicular to the
Haversian canal are the Volkman
canals.
 Volkman canals also contain blood
vessels thus creating a rich vascular
supply in the
compact bonewww.indiandentalacademy.com

 Each of the concentric matrix “tubes” that
surrounds a haversian canal is known as a
lamella.
 All the collagen fibers in a particular
lamella run in a single direction,
while collagen fibers in adjacent
lamellae will run in the opposite
direction. This allows bone to better
withstand forces.

 Osteons which are incomplete
lamellae called interstitial lamellae.
 These fill the gaps between osteons
or are remnants of
bone remodeling.

There are also circumferential lamellae that extend around the
Circumference . There are inner circumferential
lamellae surrounding the endosteum and outer circumferential
lamellae just inside the periosteum

COMPOSITION OF BONE
 Definition of bone : Bone is the specialized
mineralized connective tissue consisting
45% Inorganic material, 30% organic
material and about 25% Water. (Schroeder H.E
1976)
 By volume the proportions are 23%, 37%
and 40% respectively. (Schroeder H.E 1976)

INORGANIC COMPONENT
 It is principally composed of minerals
calcium and phosphate along with
hydroxyl, carbonate, citrate, and trace
amounts of other ions.(Glimcher MJ.1990)
 The mineral phase is in the form of
hydroxyapatite.

 They are needle- like crystallites or
thin plate of 8nm thickness and their
length is variable.
 They constitute approximately 2/3rd
of the bone structure.
 It is a naturally occurring form of
calcium apatite with the formula
Ca10(PO4)6(OH)2 to denote that the
crystal unit cell comprises two
molecules

crystal lattice of
hydroxyapatite is
hexagonal or
pseudohexagonal
Higher concentrations
of flourine and a higher
calcium-to-phosphate
ratio, increases the
biologic stability of the
molecule (Clifford R. Wheeless,)

ORGANIC COMPONENT
 About 90% of the organic material is in
the form of type I collagen
 In addition there are small amounts of
other protiens like osteonectin,
osteocalcin, osteopontin and
proteoglycans,

 Two small molecular weight chondroitin
sulphate proteoglycans have been identified
in alveolar bone. Namely decorin and
biglycan (Waddington and embry 1991)
 Osteoblasts synthesize and regulate the
deposition of collagen type 1, proteoglycan,
osteonectin, osteocalcin, bone sialoprotiens
& osteopontin (Gage et al 1989)

 Collagen type I, is the most abundant
collagen of the human body. It is present
in scar tissue, the end product when
tissue heals by repair. It is found in
tendons, skin, artery walls, the
endomysium of myofibrils, fibrocartilage,
and the organic part of bones and teeth

Collagen 1 formation.
 Three peptide chains are formed 2 alpha-
1 and 1 alpha-2 chain in ribosomes along
the Rough Endoplasmic Reticulum
(RER).
 These peptide chains (known as
preprocollagen) have registration
peptides on each end;

 Peptide chains are sent into the lumen
of the RER
 Signal Peptides are cleaved inside the
RER and the chains are now known as
procollagen
• Hydroxylation of lysine and proline
amino acids occurs inside the lumen.
This process is dependent on Ascorbic
Acid (Vitamin C)www.indiandentalacademy.com

 Glycosylation of specific hydroxylated
amino acid occurs
 Procollagen after triple helical
structure is formed is shipped to the
golgi apparatus, where it is packaged
and secreted by exocytosis.

Outside the cell
• peptides are cleaved and tropocollagen is
formed by procollagen peptidase
• Multiple tropocollagen molecules form
collagen fibrils, and multiple collagen fibrils
form into collagen fibers
• Collagen is attached to cell membranes via
several types of protein, including fibronectin
and integrin

OTHER PROTEINS ASSOCIATED WITH
BONE
 Osteonectin : It is a acid phosphate
containing glycoprotein composed of a
singe polypeptide chain and having a
strong affinity for calcium ions and type 1
collagen. (Sage and Borstein 1991)
 It has also been found in PDL around
sharpey’s fibers (Matsuura et al 1995)

 Osteocalcin : Also called as Bone
g1a protien, because it contains
gamma-carboxyglutamic acid
residues secreted by osteoblasts (Mariotti
1993)
 They act as calcium binding sites and
play a crucial role in mineralization
(Gage et al, 1989) www.indiandentalacademy.com

• Bone Sialoprotein protein : It is also
known as BSP II , a phosphoglycoprotein
containing 20% of the sialic acid residues
(Bilezikian et al, 1996).
•BSP expression marks a late stage of
osteoblastic differentiation and early
mineralisation stage. (Lekic et al, 1996)

 Although exact function of BSP II is
unknown it probably acts as an
attachment factor as it has high
affinity for collagen and enhances
attachment of osteoblasts and
fibroblasts to plastic surfaces
(Fijisawa et al, 1995)

 Osteopontin : It is also called as BSP
I due to its high sialic acid content
and is a glycophosphoprotien (Macneil et al
1995)
 It functions as a inhibitior of
mineralization during periodontal
ligament formation.(Mcneil et al, 1995)

CELLS OF ALVEOLAR BONE
Classically 3 types of bone cells are described. They are:
1. The Osteoblast, which forms bone
2. The Osteocytes, with inactive
osteoblasts maintains bone
homeostasis and
3. The Osteoclasts, which resorbs bone.

OSTEOBLASTS
 They participate in synthesizing bone
organic matrix and its mineralisation.
 They respond to the circulating hormone,
growth factors, and cytokines produced
by themselves or other cells of marrow,
which play a major role in cell-cell
communication and bone maintanence

Osteoblasts can be differentiated
into subpopulations as :
1)Those that synthesize bone
matrix (Osteoid)
2) Those that line the trabacule and endostieum
3)Those that line the periosteum

 Osteoblasts are
uninucleated cells
 They are derived
from the pluripotent
mesenchymal cells
or a perivascular cell
Friedienstien AJ 1976
 Their precursor cells
are preosteoblasts
 They are plump cells
with open faced
nuclei and abundant
Basophilic cytoplasm
• Osteoblasts exhibit
presence of alkaline
phosphatase on outer
surface of their plasma
membrane which causes
hydroxyapatite
formation.

• Osteoblasts exhibit gap junctions that
connect them to neighbouring
osteoblasts and other bone cells (Doty SB 1981)
• They are active cells with extensive ER
and Golgi bodies.
• They produce bone matrix containing
collagen 1 and other protiens

 Osteoblasts control bone mineralisation in
3 levels they are
 By production of matrix vesicle
 By modifying matrix with different enzymes
 By regulating the ions available for mineral
deposition in the matrix (Wilson 1992)
 But the bulk phase mineral deposition may
not require the matrix vesicles (Sela J et al 1992)

 Because of their multiple functions
osteoblasts are regulated by
hormones such as PTH,
1,25dihydroxy cholecalciferol,
24,25dihydroxy cholecalciferol,
estrogen, growth hormone, and
thyroxin.
 They also respond to growth factors
and cytokines.
 TGF- β and IGF-1 are produced by
osteoblasts indicating both autocrinewww.indiandentalacademy.com

 The development phases of osteoblasts can
be differentiated in 3 phases.
 Initial proliferation phase characterized by
synthesis of extracellular matrix (0 to 15 days)
 Matrix maturation phase that starts after
proliferation ceases (days 16 to 20)
 Mineralization of the matrix begins (days 20 to
25)
(stein GS 1989) www.indiandentalacademy.com

 As osteoblasts secrete bone matrix some
of them become entrapped in lacunae and
are called osteocytes.
 After their formation the osteocytes
gradually reduce in size
 They create a space immediately around
them called osteocytic lacunae.
 Narrow extensions from these lacunae

Canaliculi. They house radiating osteocytic
process.
 Osteocytes are considered to be nerve
cells of bone, maintaining balance
between resorption and remodeling (Aaren EM
1994).
 Osteocytes are sensitive to the
mechanical strain and can transude it into

 They transfer signal to the other cells through
canaliculi via secretions like PGE2 and nitric
oxide. (Nijwide PJ 1996)
 Osteocytes maintain contact with osteoblasts,
haversian canals, Periosteum and
endosteum by their canaliculi.
 The osteocyte and osteoblast together form a
functional syncytium. For prevention of
hypermineralization

Diagrams showing Osteocytes and Osteoblasts

OSTEOCLASTS
Oseteoclasts are:
 A cell responsible for resorption of the extra
cellular bone matrix
 They are Multi nucleated bone cell.
 The nuclei numbers and their size is directly
related to the degree of bone mineralization.
 They can be easily identified under light
microscopy.
 They are terminally differentiated and do not
proliferate

• They are attached to the mineralized matrix
and they are fragile due to their large size
• It’s a highly motile cell that attaches to, and
migrates along the interface between bone
and marrow
• It is formed by asynchronous fusion of
mononuclear macrophage cells
• They are found against the bone surface,
occupying shallow, hollowed out depressions
called Howships Lacunae.
• Under electron microscopy the cell membrane
shows a myriad of folds termed ruffled border

• The ruffled border corresponds to the area of
ion transport and protein secretion, its also
known as apical membrane
• The basolateral membrane is on the opposite
side of the
apical membrane
containing receptors.

Factors that increase the Osteoclast production
are :
RANKL, Macrophage CSF, Annexin II, IL-I,
Osteoclasts were shown to be derived from
Granulocyte Macrophage progenitor cell when
activated in the RANKL, macrophage CSF and
dexamethasone. (Sela J et al 1992)
Annexin II, IL-I are the factors that cause
increase in the precursor cell numbers and
osteoclasts (Dallas M, Calland JW 1995)

 When activated the osteoclast is attached
to the mineralized bone matrix by forming
a tight ringlike zone of adhesion called
sealing zone
 The sealing area forms a bone resorbing
compartment, which is a area between
osteoclast cell membrane (apical
membrane) and the resorbing bone matrix
surface.
 The osteoclast secretes proteolytic
enzymes and exudes protons (to lower
pH) into this resorbing compartment.www.indiandentalacademy.com

 Ultra structurally At the periphery of the
ruffled border the cytoplasm is devoid of
any organelles and is called clear zone.
 The clear zone is rich in fibrillar protien
actin and myosin which help in cell
adhesion to bone matrix
 The reminder of the osteoclast is heavily
laden with mitochondria that is useful in:
 Production of citric acid
 Transient storage site for Ca and Phosphate
ions

 Osteoclasts contain less RER, Golgi
apparatus are well developed (Baron R et al 1988),
There are primary
lysosomes
 Osteoclast activity : They actively
synthesize the lysosomal enzymes that
are transported through the golgi to the
ruffled border region in form of vesicleswww.indiandentalacademy.com

 These vesicles then fuse exclusively with
the plasma membrane of the ruffled border
and release their content into the bone
resorbing compartment. (Baron R, Neff L 1988)
 The enzymes that these vesicles carry are
acid phosphatase, aryl-sulfatase, beta
gluconuridase, and protienases like
cathepsin B and L . (Delisse JM 1991)
 The enzymes cause helican collagen
degradation in acidic environment. (Delisse JM
vaes G 1992)

• Tissue plasminogen activator and
collagenase (matrix metalloprotienases) are
also synthesised by osteoclasts. (Grills BL, 1990)
• Acidification of the bone resorbing
extracellular compartment is the most
important feature of osteoclastic activity (Baron R
arneet TR 1989)
• The H+ ATPase transports protons across

 It has been suggested that hormones /
local factors activate osteoclasts to start
bone resorption .
 The calcium concentration in the bone
resorbing compartment reaches a
threshold level then calcium sensors open
a novel type of channel (Zaidi M, maiauchi A 1991)
 Increase in intracellular calcium will cause
the osteoclast to deactivate and detach
from a perticular site
 Calcium is released extracellularly to
diffuse into the fluids. Completing
resorption processwww.indiandentalacademy.com

Bone membranes
Periosteum - double layered
membrane covering outer surface of bone
– outer fibrous layer
– inner osteogenic layer contains
osteoblasts and osteoclasts
Endosteum - lines trabeculae
of spongy bone and internal structures
– some connective tissue
– osteoblasts and osteoclasts

BONE MARROW
 In adults the bone marrow in the jaws are
mostly evolved into fatty or yellow inactive
type of marrow.
 But foci of red bone marrow are occasionally
seen in jaws they are in maxillary tuberosity,
maxillary and mandibular premolar and molar
areas and the mandibular symphysis and
ramus region

INTERDENTAL SEPTUM
 It consists of cancellous bone bordered by the
alveolar bone proper or cribriform plate of
approximating teeth and facial and lingual
cortical plates.
 If the interdental space is narrow the septum
consists of only the cribriform plates.
 The alveolar crest is found from 0.75mm to 1.49
mm (avarage of 1.08 mm) below the level of the
CEJ in young adults.
 This distance increases with age to an average
of 2.81 mm

 If you draw a line connecting the CEJ of
adjacent teeth, this line should be parallel to
the alveolar crest. If the line is not parallel,
then there is high probability of periodontal
disease.
 Mesiodistal and faciolingual dimensions and
shape of interdental septum depends on size
and convexity of the two approximating
crowns

OSSEOUS TOPOGRAPHY
 The height and thickness of the facial and
lingual bone plates are affected by the
alignment of the teeth and occlusal forces
 On teeth with labial version, margin of labial
bone is located farther apically. Bone margin
is thinner to a knife-edge with more
accentuated arc.
 On teeth with lingual version facial bony
plate is thicker than normal. The margin is
blunt, rounded and horizantal

BONE REMODELLING
• Modeling is a process by which bone
reshapes itself to create an organ with
maximal compressive strength.
• Bone remodeling is a life long process
where old bone is removed from the skeleton
(a sub-process called bone resorption) and
new bone is added (a sub-process called
bone formation). These processes also
control the reshaping or replacement of bone
during growth and following injuries.
Remodeling responds to functional demands
and muscle attachments. As a result bone is
added where needed and removed where itwww.indiandentalacademy.com

 The termination of resorption process and
initiation of bone formation involves a
coupling mechanism. Which is the
fundamental principle of remodeling
process (Parfitt 1982)
 Bone remodeling process involves cells of
two different lineages ie, osteoblasts and
osteoclasts. (Sodek J Mckee MD 2000)www.indiandentalacademy.com

 Bone modeling process is continuous and
covers a large surface area, while
remodeling is cyclical and usually covers a
small area. (Parfitt AM 1983)
 The current concept of bone remodeling
hypotheses' that osteoclastic precursors
become differentiated first into osteoclasts
causing bone resorption and this phase is

Followed by a bone formation phase.
(Ericksen P Charles EF 1987)
 The termination of bone resorption and the
initiation of bone formation in the
resorption lacunae occur through coupling
mechanism. (Parfitt AM 1982.)
 The Detailed nature of the activation and
coupling mechanism is unknownwww.indiandentalacademy.com

 But the coupling process is activated and
maintained by some growth factors like
lymphokines, Fibroblast growth factor,
TGF β, prostaglandins, and hormones (
Pilbeam CC et al 1989)
 Whether activation of osteoblasts begin
simultaneously with osteoclastic
recruiment is still unknown.www.indiandentalacademy.com

 As remodeling involves bone formation and
resorption we look into factors of formation :
 Factors Regulating Bone Formation :
 Formation of bone involves 2 major steps
 Production of new organic matrix {osteoid} by
osteoblasts
 Mineralization of that matrix
 Bone formation is controlled by both

 The local factors are growth factors that
act directly on cells of osteoblastic linage.
And they are both autocrine and paracrine
in function. (Canalis E Mcarthy T 1989)
 Systemic hormones act directly on
osteoblastic linage or by stimulating the
production of growth factors,

 Common features of Growth factors that
regulate bone formation :
 They are polypeptides
 They bind to specific receptors for their
activity
 They act locally
 They are natural products of cells
 They are multifunctional ( Yu X Antoniades 1993)
 Platelet Derived Growth Factor(PDGF)
 Heparin Binding Growth Factors
 Transforming Growth Factors (TGF)
 Bone Morphogenic Proteinswww.indiandentalacademy.com

 Factors Regulating Bone Resorption
 The bacterial factors and host factors are
responsible for bone resorption
Bacterial Host Osteotropic
Cytokines
Capsular and surface
associated material
PGE2 Interlukin 1 & 6
Lipopolysaccharides Leukotrienes Tumour necrosis factor
Lipothecoic acid Heparin Transforming growth
factor
Peptidoglycan Thrombin Platelet derived growth
factor
Lipoprotien Bradykinin Gamma interferon
Elly and Manson

REGULATION OF BONE RESORPTION
Elly and manson

 Regulation of bone by Systemic
hormones
 Parathyroid harmone
 1,25 Dihydroxyvitamin D3
 Calcitonin
 Estrogens

Hormonal control of remodelling
•Hormonal control of remodelling acts to
maintain blood calcium homeostasis rather than
integrity of skeleton
Blood calcium homeostasis
– Parathyroid hormone (PTH) released when
blood Ca2 low - stimulates osteoclasts
Also promotes Ca2 absorption in GI tract and
reduces filtration at kidneywww.indiandentalacademy.com

Calcitonin is released when blood
Ca2 is high
•inhibits osteoclasts
•stimulates osteoblasts

Released by the C cells of the thyroid gland in response to
high blood [Ca2+].
•Calcitonin acts to “tone down” blood calcium levels.
•Calcitonin causes decreased osteoclast activity which
results in decreased break down of bone matrix and
decreased calcium being released into the blood.
•Calcitonin also stimulates osteoblast activity which means
calcium will be taken from the blood and deposited as
bone matrix.
Effect of Calcitonin

 Theories about bone resorption
 Resorption was thought to be brought about
by PTH, PGE2, 1,25-(OH)2 D3, or IL-1 via
direct action of them on osteoclasts and
osteoblastic precursors.
 In 70’s there was a coupling theory put
forward for remodeling process.
 TGF and PTH is considered as the main
growth factor in the coupling process.
 Recent studies have suggested that coupling
process is more directly involved by TNF
ligand family called RANKL on the
membranes of osteoblasts.

 Osteoclast precursors express RANK, a
TNF receptor family member that
recognise RANKL through cell to cell
interaction.
 In addition to RANKL, osteoblasts also
secrete osteoprotogerin that inhibits
osteoclastogenesis. It acts as a decoy for
RANKL.

CLINICAL CONSIDERATIONS
 Agents that block the differentiation or
activity of osteoclasts are potential
therapeutic agents.
 OPG (osteoprotegerin) acts as a decoy
receptor that blocks RANKL and RANK
juxtacrine interaction.
 NSAIDS and other antiinflammatory drugs
can inhibit differentiation of
hematoprogenitor cells into pre-
osteoclasts.

 Bisphosphonates and chemically modified
doxycycline also inhibit the RANK receptor
on osteoclasts thus reducing bone
resorption

 Fenestration and Dehiscence. :
 Fenestrations : are the isolated areas where the
root surface of the teeth are denuded of bone,
except it is covered by periosteum and gingiva. (
In these areas the marginal bone is intact.)
 When the fenestration extend to the marginal
bone the defect is called as Dehiscence.
 They are found more on buccal than lingual
bone, Anterior teeth is more involved than
posterior and are frequently bilateral.

Fenestration and Dehiscence on
premolar and canine roots respectively

Nerve supply
 The nerve supply originates from the inferior
or the superior alveolar nerves.
 The fibers enter from the apical region and
lateral socket walls.
 The apical region contains more nerve
endings (except Upper Incisors)

 Blood supply to the alveolar bone is derived
from the superior and inferior alveolar
arteries.
 The blood supply increases from the incisors
to the molars
 The venous drainage accompanies the
arterial supply.
 Lymphatics from the junctional epithelium
drain into the periapical region and from
there they pass through alveolar bone to
inferior dental canal or infraorbital canal to
drain into submaxillary lymph nodeswww.indiandentalacademy.com

Bibliography :
1.Clinical Periodontology Carranza 10th edition
2.Periodontics Elly’s and manson
3.Essentials of Periodontics Kornman and wilson
4.Oral Anatomy and Histology Ten cate
5. Sampathnarayan and Bartold

Alveolar bone

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